Formation and delivery of an atomized liquid

ABSTRACT

A method of delivering an atomised liquid including supplying a liquid to an admixing chamber (3,34), separately supplying a compressed gas to the admixing chamber (3,34), the compressed gas at least substantially completely evacuates the liquid held in the admixing chamber and delivering the liquid through an atomising device (4,5,60) to atomise the liquid, wherein the quantity of the liquid and the compressed gas supplied to the admixing chamber (3,34) is controlled to thereby maintain a predetermined mass ratio of the liquid and the supplied compressed gas. An apparatus for delivering an atomised liquid including a liquid supply device (6,24) for supplying liquid to an admixing chamber (3,34), a gas supply device (2,33) for separately supplying compressed gas to the admixing chamber (3,34), and an atomising device (4,5,60) for atomising the liquid evacuated by the supplied compressed gas, wherein the liquid supply device (6,24) supplies a predetermined quantity of liquid at each actuation of the apparatus and the gas supply device (2,33) controls the quantity of gas supplied to the admixing chamber (3,34) to thereby maintain a predetermined mass ratio of the liquid and the supplied compressed gas.

This invention relates to a method and apparatus for the formation anddelivery of an atomised liquid. This invention is applicable foradministering a drug dosage to a human or an animal by way of inhalationof the drug dosage through the respiratory tract.

It is well known to administer drugs to humans through the respiratorytract. Conventional methods of such administration utilise inhalerswhich the user places in the mouth and inhales during the release of thedrug dosage from the inhaler. Such inhalers normally use Freon as themeans by which the drug is sprayed into the mouth of the user. The drugto be administered is either dissolved or carried in solid or liquidsuspension by the Freon. Upon release from the inhaler, the Freonvaporises and propels the drug into the users mouth.

Normally, the effectiveness of the drug is related to the amount of thedrug that actually passes through the mouth and throat of the user andwhich is deposited on the lower respiratory tract. It is common todefine the effectiveness of the drug delivery system in terms of"percentage respirable dose". The higher the percentage respirable dose,the better the ability of the system to deliver the drug to where it ismost effective. Apart from the obvious benefits of having a highpercentage respirable dose in that there is less wastage of what in manyinstances is a relatively expensive respirable drug, there is anadditional benefit in that there will be reduced side-effects from therespirable drug being absorbed in the mouth or upper respiratory tractor being transported to the users digestive system. Futher, there is atthe present time an imperative for new systems of administering a drugdosage to humans or animals which preferably do not use propellants suchas Freon (which is believed to be environmentally harmful due to itseffects on the earth's ozone layer) and which are capable of achievingthe required percentage respirable dose. It is therefore an object ofthe present invention to provide an improved method and apparatus fordelivering atomised liquids. A preferred object is to provide a methodand apparatus for delivering a respirable drug capable of achieving ahigh percentage respirable dose.

The present invention therefore provides in one aspect a method ofdelivering an atomised liquid including supplying a liquid to anadmixing chamber, separately supplying a compressed gas to the admixingchamber, the compressed gas at least substantially completely evacuatingthe liquid held in the admixing chamber and delivering the liquidthrough an atomising means to atomise the liquid, wherein the quantityof the liquid and the compressed gas supplied to the admixing chamber iscontrolled to thereby maintain a predetermined mass ratio of the liquidand the supplied compressed gas.

Liquid may be supplied to the admixing chamber subsequent to thecompressed gas. Alternatively, compressed gas may be supplied to theadmixing chamber subsequent to the liquid. The compressed gas maycompletely entrain the liquid held within the admixing chamber. The gasmay conveniently be air although other gases are also envisaged.Preferably, the liquid contains a drug in solution or in liquid or solidsuspension for administering to the respiratory tract of a human or ananimal. Preferably, the contents of the admixing chamber pass throughthe atomising means for a predetermined duration which is less than thenormal duration of the inhalation event of a human or an animal.

Preferably, the predetermined amount and pressure of the compressed gasis selected so that the entire contents of the admixing chamber arepassed through the atomising means in a time period which is less thanthe duration of the normal inhalation event of the human or animal. Inone form of the invention, it is possible for this time period to beadjusted to suit the individual user.

Preferably, the particle size distribution of the atomised liquidproduced by release of the contents of the admixing chamber through theatomising means is such that sufficiently small particles are created soas to be readily transported to the desired part of the human's oranimal's respiratory tract during the inhalation event. In the case ofhumans, particle sizes of less than 10 microns are desirable andparticles sizes of less than 6 microns are even more desirable.

According to another aspect of the present invention, there is providedan apparatus for delivering an atomised liquid including a liquid supplymeans for supplying liquid to an admixing chamber, a gas supply meansfor separately supplying compressed gas to the admixing chamber, and anatomising means for atomising the liquid evacuated by the suppliedcompressed gas, wherein the liquid supply means supplies a predeterminedquantity of liquid at each actuation of the apparatus and the gas supplymeans controls the quantity of gas supplied to the admixing chamber tothereby maintain a predetermined mass ratio of the liquid and thesupplied compressed gas.

The compressed gas may completely entrain the liquid held within theadmixing chamber. Preferably, the gas supply means for supplying apredetermined amount of compressed gas to the admixing chamber includesa gas reservoir for containing a gas at a predetermined first pressureand a valve means separating said gas reservoir from said atomisingmeans, said valve means being operable so as to allow the gas to flowfrom the gas reservoir through the admixing chamber and the atomisingmeans until a second pressure level is achieved due to the substantialequilibrium being achieved between the atmospheric pressure and thepressure in the gas reservoir. The gas reservoir may have a set volumewhich contains an at least substantially predetermined mass of gas whenthe compressed gas is at the predetermined first pressure. Thecompressed gas may be provided by a compressor pump communicating withthe gas reservoir. The compressed gas may be supplied through anon-return valve into the gas reservoir. The rate of supply ofcompressed gas to the admixing chamber may be significantly greater thanthe rate of supply of compressed gas from the compressor pump to the gasreservoir.

In an alternative embodiment, the gas supply means may include a gasreservoir for the supply of gas at a predetermined first pressure, valvemeans being provided between the gas reservoir and the atomising meansand being operable to control the admixture and evacuation of the liquidand the gas in the admixing chamber, the required control over the massof gas being achieved at each actuation of the apparatus by controllingthe duration of the opening of the valve means to admit gas to theatomising means so as to control the quantity of gas delivered inrelation to the fixed mass of liquid dispensed into the admixingchamber, a predetermined second pressure being defined at the closure ofthe said valve means at the end of the actuation of the apparatus. Thepredetermined second pressure may be a function of the size of the gasreservoir relative to the size of the restriction of the atomisingmeans.

The atomising means may preferably be an atomising nozzle having acircular throat portion with a preferred throat diameter lying in therange of between 0.15 millimetres to 0.35 millimetres. A downstreamdivergent duct may be provided expanding out from the throat portion atan included angle lying between 2 degrees and 8 degrees. The axiallength of the divergent portion downstream of the throat diameter maypreferably be between 0.5 millimetres and 5 millimetres.

Actuation means may be provided for displacement of the valve means. Theactuation means may include a pushrod for displacing the valve means.The pushrod may be moved by way of a solenoid actuator. Alternatively,the actuation means may include a manually actuated pushrod.

The liquid supply means preferably includes a flexible bladder forcontaining the liquid, a body member having a liquid chamber incommunication with the flexible bladder, a piston means supported withinthe liquid chamber for pumping liquid contained within the liquidchamber to the admixing chamber, and a protective outer shroud forenclosing the flexible bladder and body member, wherein displacement ofthe outer shroud produces a relative displacement of the piston withinthe liquid chamber to thereby pump the liquid from the liquid chamber. Acontinuing displacement of the outer shroud preferably subsequentlyresults in displacement of the pushrod after the liquid has been pumpedfrom the liquid chamber into the admixing chamber. The pushrod mayinclude an elongate passage therethrough and at least one dischargeorifice extending therefrom, the liquid being pumped through theelongate passage and out of the discharge orifice into the admixingchamber. A floating valve ring may preferably be provided in a annulargroove in said piston, the floating valve ring sealing the fluid chamberwhen the piston is displaced in a first direction, and allowing fluidcommunication with the fluid chamber when the piston is displaced in anopposing direction thereof.

According to another aspect of the invention, there is provided a liquidmetering device including a flexible bladder for containing liquid, theflexible bladder surrounding a body member having a liquid chambertherein, the liquid chamber being in fluid communication with theinterior of the flexible bladder, an outer shroud for containing theflexible bladder and the body member, a piston supported within theliquid chamber for pumping liquid therefrom, and a pushrod extendingfrom the piston, wherein movement of the outer shroud relative to thepiston results in relative displacement of the piston within the liquidchamber to thereby pump liquid from the liquid chamber. The pushrod maybe displaced together with the piston after the liquid has been pumpedfrom the liquid chamber.

The piston may be integral with the pushrod. Alternatively, in anotherembodiment, the piston may be integral with the body member, the liquidchamber being provided within the pushrod. The pushrod may include anelongate passage passing therethrough, the pumped liquid passing throughthe passage to at least one discharge orifice provided on the pushrod. Anon-return valve may be supported within the passage for controlling thedirection of flow of liquid therethrough.

The apparatus may include a floating valve ring provided in an annulargroove in the piston, the floating valve ring sealing the liquid camberwhen the piston is displaced in a first direction, and allwing fluidcommuniation with the liquid chamber when the piston is displaced in anopposing direction thereof.

It has been found that the method and apparatus of the present inventionmay atomise liquids such as water or alcohol such that the particlesproduced in the resultant spray may not impinge in the upper regions ofthe throat of the user to the same extent as found in existing metereddose inhaler apparatus using liquid Freon propellents to disperse drugagents in a spray developed by rapid evaporation of a liquid propellent.

It has also been found that in relation to the method and apparatus ofthe present invention, a constant gas pressure is not as important tothe function of the apparatus as the requirement of a controlled ratioof the mass of gas relative to the mass of dispersed liquid to passthrough the atomising nozzle, even though gas pressure may be aconvenient means of specifying a gas mass in the apparatus which may bedispensed during an inhalation event. The temperature of the gas is ofsecondary importance and, in practice, the temperature of the portableapparatus is typically in the relatively narrow range of environmentalconditions defined by the comfort conditions of typical human patients.

It will be of convenience to further describe the invention by referenceto the accompanying drawings which illustrate possible embodiments ofthe invention. Other embodiments of the invention are possible andconsequently the particularity of the accompanying drawings is not to beunderstood as superseding the generality of the preceding description ofthe invention.

In the drawings:

FIG. 1 shows a diagrammatic representation of the human respiratorytract;

FIG. 2 shows a graph showing the Percentage Respirable Dose against theratio of Mass of Air to Mass of Liquid;

FIG. 3 shows a diagrammatic representation of a first embodiment of theapparatus according to the present invention;

FIG. 4 shows a diagrammatic representation of a second embodiment of theapparatus according to the present invention;

FIG. 5 shows a diagrammatic representation of a third embodiment of theapparatus according to the present invention;

FIG. 6 shows the pushrod and piston assembly of the apparatus of FIG. 5;and

FIGS. 7 to 10 show alternative embodiments of the liquid metering deviceaccording to the present invention.

Referring initially to FIG. 1, label A refers to the mouth of a humanpatient into which the spray nozzle is inserted at each dosing event.Label B refers to the throat region where a large portion of a spray mayimpinge and not reach the lower regions of the respiratory tract. LabelC refers to the general region where the drug is to be deposited. Therespirable dose passes to this general region, while the impingedportion in the throat may pass to the digestive system and cause certainunwanted side effects in a patient.

Regarding FIG. 2, there is shown a graph detailing the experimentalinformation derived from analytical tests of an embodiment of thisinvention to atomise aqueous sprays. In FIG. 2 it may be derived thatthe control over the mass ratio results in effective control over thepercentage of the spray which is respirable by the patient. Further, thedroplet size distribution produced by the nozzle means described in thisinvention results in a high maximum percentage respirable dose due tothe small droplets produced. It is noted that higher mass air/liquidratios provide significant improvements in the respirable dose possible.

Referring to FIG. 3, a first embodiment of the apparatus is illustratedshowing an atomiser body 1 having a reservoir 2 which supplies gas to anadmixing chamber 3, into which a discrete dose of liquid may bedispensed from the liquid metering device entrain from the reservoir 2may entrain the liquid in the space 7 leading to the throat 4 of theatomising nozzle. The divergent duct 5 downstream of the throat 4provides the final path of the atomised liquid and gas which areultimately directed entirely to the mouth A of the human patientdepicted in FIG. 1. Valve means are provided in the path between thereservoir 2 and the throat 4 of the atomising nozzle, such means beingdefined by the spherical valve element 9 which is normally urged intosealing engagement with the valve seat 8 by the spring 10.

A solenoid 11 having a ferromagnetic path 14, windings 15 and a movablearmature 13 with an integral pushrod 12 is used to control the gas flowto the admixing chamber 3. The solenoid 11 is actuated by applying anelectric current to the windings 15 so as to provide an electromotiveforce on the armature 13. This force is transmitted by the pushrod 12 toovercome the force of the spring 10 acting on the valve element 9 and tothereby allow gas to flow from the reservoir 2 to the admixing chamber3.

The quantity of gas supplied during an actuation event of the solenoid11 is controlled by the volume of the reservoir 2 and the pressure towhich the reservoir 2 is charged by the compressor pump 16. A non-returnvalve 17 is provided between the compressor pump 16 and the reservoir 2and includes a spherical valve element 19 acting on a sealing seat 18due to the force imparted thereto by the spring 20.

The pressure supplied to the reservoir 2 may be controlled by regulatingthe actuation of the compressor pump 16 by sensing the pressure in thereservoir 2 with the sensor 21 connected by a duct 22 to the reservoir2. In practice, the pressure sensor 21 may take the form of apressure-sensitive switch controlling the flow of electrical current tothe compressor pump 16 so that the compressor pump 16 is deactivatedwhen a sufficiently high pressure is reached.

The rate of re-supply of gas to the reservoir 2 is conveniently lowerthan the rate at which the gas is drained during an actuation event ofthe solenoid 11, so that the pressure in the reservoir 2 falls to a lowvalue close to the equilibrium pressure with atmospheric pressuredownstream of the nozzle duct 5. The mass of gas supplied to theadmixing chamber 3 is thus relatively dependent on the size of thereservoir 2 and the pressure to which it is charged at the start of theactuation event. The mass of gas supplied is relatively independent ofthe smaller rate of supply which is available from the compressor pump16.

Alternatively, the reservoir 2 may be made of sufficient size to drop inpressure by a predetermined amount in response to an actuation event ofthe solenoid 11, where the duration of the current flowing in thewindings 15 may be controlled so as to limit the mass of gas deliveredto the admixing chamber 3.

In relation to the atomising nozzle, the nozzle has a diverging section5 downstream of the restrictive throat 4, which has a desirable effectin obtaining the atomisation demonstrated in this apparatus, theefficiency of which is partly due to the high velocity of the gas flowwhich is produced by the divergent section. Also, the diverging portionis desirable in simplifying the manufacture of the nozzle by low-costtechniques.

As shown in FIG. 4, the valve element 9 and associated seat 8 and spring10 may be alternatively located downstream of the location of theintroduction of the liquid from the liquid metering device 6. All otherdetails and principles of operation are similar to the correspondingparts as enumerated in FIG. 3.

The above two embodiments of the invention are particularly applicablefor automatic operation because a solenoid valve 14 is used to actuatethe valve element 9. It is however also possible to have a manuallyactuated apparatus as shown in FIGS. 5 and 6. Referring initially toFIG. 5, the liquid metering device 24 of the apparatus includes a firstchamber 31 for storing liquid 38, and a second chamber 32 providedwithin a cylindrical body 29 in fluid communication with the firstchamber 31. A gas reservoir 33 and an admixing chamber 34 are providedin a base portion 23 of the apparatus.

The first chamber 31 is formed by a flexible plastic bladder 35contained within a protective outer shroud 36 with at least one venthole 37 which allows atmospheric pressure to bear upon the first chamber31. The liquid 38 to be dispensed is contained within the first chamber31 and communicates with the second chamber 32 through holes 39 and 40provided through a collar 25 surrounding the cylindrical body 29 and thepiston valve port 41. The second chamber 32 provides metering of themass of liquid supplied to the admixing chamber 34.

As shown in FIG. 6, the piston valve port 41 includes a piston 42, whichis effectively an extension of the pushrod 43. The piston 42 has anannular groove 23 at the upper end thereof which defines two separatepressure lands, the sealing land 44 and the retraction land 45. Theretraction land 45 is part of a crown 46 which allows fluid to alwayspass through the clearance 47 between the crown 46 and the bore 49 ofthe pumping chamber defining the second chamber 32. A flexible valvering 48 is engaged in the bore 49 and selectively cooperates between theaforementioned pressure lands 44 and 45, the actual contact of the valvering 48 with the respective lands 44 and 45 depending on the directionof relative motion of the piston 42 within the bore 49. Because thevalve ring 48 does not fill the groove 23, only one of the respectivelands 44 or 45 can be in axial contact with the sealing ring 48 at anyone time.

During a pumping stroke, the entire shroud 36 and associated parts,including the bore 49 are moved by manual axial force in the generaldirection indicated by the arrow A. A reaction force maintained on thepushrod 43 by the valve member 50 and associated spring 51 of FIG. 5results in the volume of the second chamber 32 decreasing and the valvering 48 making contact with the sealing land 44. Because the volumedecreases in the second chamber 32, the liquid pressure rises to such anextent that the relief valve 55 becomes unseated, allowing liquid topass from the second chamber 32, past the port 54 and the relief valve55, through the coils of the spring 56 and into the pushrod duct 53. Thespring 57 is compressed as the delivery stroke continues, until thepiston crown 46 makes contact with the stop face 58. Up to this event,the liquid dose passes from the pushrod duct 53, through the orifices 59and into the admixing chamber 34, which is normally in equilibrium withatmospheric pressure due to the discharge port 60 communicating with theatmosphere.

At this point the axial force exerted by the pushrod 43 may overcome thecombined forces on the valve element 50 due to the spring 51 and theelevated gas pressure in the gas reservoir 33. The valve element 50 mayopen and allow high pressure gas in the gas reservoir 33 to escape intothe admixing chamber 34 and entrain the liquid 38 therein as the gasmoves to the venting discharge port 60 as the pressure equilibrium isachieved. Atomisation is achieved across the discharge port 60 as therelatively higher velocity gas moves over the surface of the relativelylower velocity liquid.

The stored quantity of gas in the gas reservoir 33 is of a discretequantity due to the fixed volume of the reservoir 33 and a relativelyfixed pressure and temperature, although very close control overpressure and temperature is not strictly required for the purposes ofthis invention. The pressure may be achieved by an electrically-drivencompressor or hand pump.

When the manual actuation of the shroud 36 is released, the returnspring 57 returns the piston 42 to the quiescent position defined bycontact of the land 61 on the piston 42 with the land 62 on the bore 49.In fact, the shroud 36 and associated parts move vertically in the senseof FIG. 5. As the piston 42 and shroud 36 move in the direction urged bythe spring 57, the valve ring 48 makes contact on the retraction land45. Liquid is allowed to enter the second chamber 32 past the definedport 63 in the piston crown 46. In this state, the quiescent state,liquid may fill the second chamber 32 in preparation for the nextdelivery stroke.

Seal 64 and seal 65 act to prevent the escape of fluids in an obviousmanner.

It is envisaged that more than one port 63 may be used in the crown 46and that various shapes may be used to the same effect as the one detailshown in FIG. 6.

Furthermore, it is envisaged that an improved discharge port 60 may beemployed to obtain optimum atomisation. The surface area exposed to theliquid may be increased relative to the exit area of the port 60,thereby increasing the velocity of the gas and liquid relative to oneanother, thus improving the atomisation. Alternatively, an atomisationnozzle as shown in FIGS. 3 and 4 could be used.

The gas supply to the reservoir 33 may be accomplished by apositive-displacement air pump driven by an electric motor or solenoidwhich may fill the chamber relatively slowly between actuation events,the control of which may be exercised by turning off the electric pumpwhen the pressure in the chamber has reached a predetermined pressure.The air supply to the reservoir 33 through the check valve 66 may beretained between air pumping events by the non-return characteristics ofthe check valve 66.

The above described arrangement allows actuation of the apparatus evenwhen the apparatus is held in a position away from vertical. The liquidmetering device 24 meters the correct amount of liquid and is unaffectedby the orientation of the apparatus. Furthermore, the storing of theliquid 38 within the flexible bladder 35 helps to ensure that the liquid38 remains sterile. Once the flexible bladder 35 is fully emptied ofliquid 38, the liquid metering device 24 can optionally be disposed ofand replaced with a new liquid metering device.

Alternative embodiments of the liquid metering device 24 are shown inFIGS. 7 to 10, with like reference numerals being used for correspondingfeatures. In the embodiment shown in FIG. 7, the primary difference isthat the flexible bladder 35 is affixed by a ring 70 to a radiallyextending member 71 of the pushrod 43. This provides a more secure sealfor the flexible bladder 35 as well as making the liquid metering device24 more easy to manufacture. The liquid in the pushrod duct 53 mayberetained therein between actuation events by the surface tension of theliquid within the discharge orifices 59. Alternatively, the liquidmetering device 24 may be designed to positively contain the liquidwithin the pushrod duct 53 close to the discharge orifices 59. Such aconstruction is shown in FIG. 8.

In FIG. 8, the check valve element 80 is in the form of a poppet valvelocated close to and normally closing the discharge orifices 59. Atension spring 81 is supported between a spring mount 82 located withinthe pushrod duct 53 and the check valve element 80. This arrangementmaintains the fluid within the pushrod duct 53 until the liquid is to bedispensed. It is envisaged that the collar 25 may be constructed of aductile and malleable material which may be deformed during assembly inorder to calibrate the stroke of the pump to a defined andaccurately-specified value. Furthermore, the accurately-specified strokemay be varied for different applications requiring different amounts ofdispensed fluid.

The alternative embodiment in FIG. 8 is however not as accurate in termsof delivered liquid volume as the embodiment shown in FIG. 7 but is moreeasily adjusted by external apparatus after the final assembly of theliquid metering device 24.

FIG. 9 shows another embodiment where the collar 25 of the previousembodiments is replaced in function by the external protective outershroud 36 and an end piece 26 closing off the bottom end of the shroud36. In this construction the stroke is limited by the contact of a land27 provided on the end-piece 26 with the radial extending member 71 ofthe pushrod 43 and the alternative contact of the outer shroud 36 with acontact portion of the bladder 35, and the top 28 of the cylinder body29. The axial position of the end-piece 26 within the shroud 36 may bevaried to obtain various delivered quantities of fluid.

To improve the reliability of the sealing of the bladder 35, the portionof the bladder 35 contacting the outer shroud 36 may be formed from arigid section of stronger material so that the contact force (F) istransmitted over a greater area and there is less chance of damage tothe bladder 35.

In the variant shown in FIG. 10, the piston 90 is a separate componentfrom the pushrod 43 with the piston bore being provided within thepushrod 43. The liquid metering device 24 is otherwise functionallyequivalent to the embodiment of FIG. 9.

Although the embodiments and description of the invention haveconcentrated on respiratory drug administration to human or animalpatients, it will be appreciated that the invention contemplates otherapplications where there is a desire to administer accurate amounts of aliquid in a discrete form by using a compressed gas such as air.

The claims defining the invention are as follows:
 1. A method ofdelivering an atomised liquid including supplying a liquid to anadmixing chamber, separately supplying a compressed gas to the admixingchamber, the compressed gas at least substantially completely evacuatingthe liquid held in the admixing chamber and delivering the liquidthrough an atomising means to atomise the liquid, wherein the quantityof the liquid and the compressed gas supplied to the admixing chamber iscontrolled to thereby maintain a predetermined mass ratio of the liquidand the supplied compressed gas.
 2. A method according to claim 1 liquidis supplied to the admixing chamber subsequent to the compressed gas. 3.A method according to claim 1 wherein compressed gas is supplied to theadmixing chamber subsequent to the liquid.
 4. A method according toclaim 1 wherein the compressed gas entrains the liquid held in theadmixing chamber.
 5. A method according to claim 1 wherein the liquid isa respiratory drug for administering to the respiratory tract of a humanor animal.
 6. A method according to claim 1 wherein at least a portionof the contents of the admixing chamber pass through the atomising meansfor a predetermined duration less than the normal duration of theinhalation event of a human or animal.
 7. A method according to claim 1wherein the entire contents of the admixing chamber pass through theatomising means in a predetermined duration which is less than theduration of the normal inhalation event of a human or animal.
 8. Amethod according to claim 6 wherein the predetermined duration isadjustable.
 9. A method according to claim 1 wherein the averageparticle size of the atomised liquid is less than 10 microns, preferablyless than 6 microns.
 10. A method according to claim 1 wherein thecompressed gas is air.
 11. An apparatus for delivering an atomisedliquid including a liquid supply means for supplying liquid to anadmixing chamber, a gas supply means for separately supplying compressedgas to the admixing chamber, and an atomising means for atomising theliquid evacuated by the supplied compressed gas, wherein the liquidsupply means supplies a predetermined quantity of liquid at eachactuation of the apparatus and the gas supply means controls thequantity of gas supplied to the admixing chamber to thereby maintain apredetermined mass ratio of the liquid and the supplied compressed gas.12. An apparatus according to claim 11 wherein the compressed gasentrains the liquid held in the admixing chamber.
 13. An apparatusaccording to claim 11 wherein the gas supply means includes a gasreservoir for containing gas at a predetermined first pressure and avalve means separating said gas reservoir from said atomising means,said valve means being operable so as to allow the gas to flow from thegas reservoir through the admixing chamber and the atomising means untila second pressure level is reached within the gas reservoir.
 14. Anapparatus according to claim 13 wherein the second pressure level is atleast substantially atmospheric pressure.
 15. An apparatus according toclaim 11 wherein the gas supply means includes a gas reservoir forcontaining gas at a predetermined first pressure, a valve means providedbetween the gas reservoir and the atomising means for controlling theadmixture and evacuation of the liquid and the gas in the admixingchamber, the duration of opening of the valve means being controllableto thereby control the gas/liquid mass ratio.
 16. An appartus as claimedin claim 15 wherein the compressed gas entrains the liquid held in theadmixing chamber.
 17. An apparatus according to claim 15, wherein thedelivery of gas is ceased from the gas reservoir when the gas within thegas reservoir is at a predetermined second pressure, said predeterminedsecond pressure being a function of the size of the gas reservoirrelative to a size of a restriction of the atomising means.
 18. Anapparatus according to claim 13 including a compressor pump forsupplying compressed gas to the gas reservoir, with a non-return valveprovided between the compressor pump and the gas reservoir.
 19. Anapparatus according to claim 18 wherein the rate of supply of compressedgas from the gas reservoir to the admixing chamber is relatively higherthan the rate of supply of compressed gas from the compressor pump tothe gas reservoir.
 20. An apparatus according to claim 13 wherein theatomising means is an atomising nozzle having a circular throat portionand a downstream divergent duct extending downstream therefrom.
 21. Anapparatus according to claim 20 wherein the throat portion has adiameter of between 0.15 to 0.35 millimetres.
 22. An apparatus accordingto claim 20 wherein the divergent duct extends at an included angle ofbetween 2 and 8 degrees.
 23. An apparatus according to 20 wherein theaxial length of the divergent duct is between 0.5 and 5.0 millimetres.24. An apparatus according to claim 11 wherein the liquid supply meansincludes a flexible bladder for containing the liquid, a body memberhaving a liquid chamber in communication with the flexible bladder, apiston supported within the liquid chamber for pumping liquid containedwithin the liquid chamber to the admixing chamber, and a protectiveouter shroud for enclosing the flexible bladder and body member, whereindisplacement of the outer shroud produces a relative displacement of thepiston means within the liquid chamber to thereby pump the liquid fromthe liquid chamber.
 25. An apparatus according to claim 24 including afloating valve ring provided in an annular groove in said piston, thefloating valve ring sealing the liquid chamber when the piston isdisplaced in a first direction, and allowing fluid communication withthe liquid chamber when the piston is displaced in an opposing directionthereof.
 26. An apparatus according to claim 25 including actuationmeans for displacement of the valve means.
 27. An apparatus according toclaim 26 wherein the actuation means includes a pushrod for displacingthe valve means.
 28. An apparatus according to claim 27, wherein acontinuing displacement of the outer shroud subsequently results indisplacement of the pushrod after the liquid has been pumped from theliquid chamber into the admixing chamber.
 29. An apparatus according toclaim 27 wherein the pushrod includes an elongate passage therethroughand at least one discharge orifice extending therefrom, the liquid beingpumped through the elongate passage and out of the discharge orificeinto the admixing chamber.
 30. An apparatus according to any one ofclaims 27 wherein the pushrod is moved by means of a solenoid actuator.31. An apparatus according to claim 26 wherein the actuation meansincludes a manually actuated pushrod.
 32. A liquid metering deviceaccording to claim 27, wherein the pushrod is displaced together withthe piston after the liquid has been pumped from the liquid chamber. 33.A liquid metering device according to claim 32, wherein the piston isintegral with the pushrod.
 34. A liquid metering device including aflexible bladder for containing liquid, the flexible bladder surroundinga body member having a liquid chamber therein, the liquid chamber beingin fluid communication with the interior of the flexible bladder, anouter for containing the flexible bladder and the body member, a pistonsupported within the liquid chamber pumping liquid therefrom, and apushrod extending from the piston, the piston being integral with thebody member, the liquid chamber being provided within the pushrod.wherein movement of the outer shroud relative to the piston results inrelative displacement of the piston within the liquid chamber to therebypump liquid from the liquid chamber.
 35. A liquid metering deviceaccording to claim 34, the pushrod including an elongate passage passingtherethrough, the pumped liquid passing through the passage to at leastone discharge orifice provided on the pushrod.
 36. A liquid meteringdevice according to claim 35 including a non-return valve supportedwithin the passage for controlling the direction of flow of liquidtherethrough.
 37. A liquid metering device including a flexible bladderfor containing liquid the flexible bladder surrounding a body memberhaving a liquid chamber therein the liquid chamber being in fluidcommunication with the interior of the flexible bladder an outer forcontaining the flexible bladder and the body member, a piston supportedwithin the liquid chamber for pumping liquid therefrom, a pushrodextending from the piston, and a floating valve ring provided in anannular groove in said piston, the floating valve ring sealing theliquid chamber when the piston is displaced in a first direction, andallowing fluid communication with the liquid chamber when the piston isdisplaced in an opposing direction thereof, wherein movement of theouter shroud relative to the piston results in relative displacement ofthe piston within the liquid chamber to thereby pump liquid from theliquid chamber.
 38. A liquid metering device according to claim 37,wherein the piston is integral with the body member, the liquid chamberbeing provided within the pushrod.
 39. A liquid metering deviceaccording to claim 37, the pushrod including an elongate passage passingtherethrough, the pumped liquid passing through the passage to at leastone discharge orifice provided on the pushrod.
 40. A liquid meteringdevice according to claim 39, including a non-return valve supportedwithin the passage for controlling the direction of flow of liquidtherethrough.
 41. A liquid metering device according to claim 37,wherein the pushrod is displaced together with the piston after theliquid has been pumped from the liquid chamber.